Brutalism is also about showing the materials used for the structure rather than using facades. (But I don’t think anyone is saying rough rock coverings are brutalist lol)

Depending on the coloration of the material in of the texture and how rough it is, several feet to hundreds of yards/meters away.

But the reason brutalism is easier to see far away is more about the solid rectangular shapes and style than the texture of the material. If you made a concrete version of a building normallly made of stone with lots of fine details like a cathedral it wouldn’t be considered brutalism just because it was all concrete.